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CVE-2026-31951

LibreChat's MCP Server Header Injection Enables OAuth Token Theft

Published: Mar 27, 2026Updated: Mar 30, 2026 Sources: CVE List NVDCWE-200
NVD MITRE
6.8CVSSMEDIUM
EPSS Score
0.2%
Top 84.7%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

Description

LibreChat is a ChatGPT clone with additional features. In versions 0.8.2-rc1 through 0.8.3-rc1, user-created MCP (Model Context Protocol) servers can include arbitrary HTTP headers that undergo credential placeholder substitution. An attacker can create a malicious MCP server with headers containing `{{LIBRECHAT_OPENID_ACCESS_TOKEN}}` (and others), causing victims who call tools on that server to have their OAuth tokens exfiltrated. Version 0.8.3-rc2 fixes the issue.

CVSS Vector Breakdown

AV:NAC:LPR:LUI:RS:CC:HI:NA:N
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:LPrivileges Required
Low
UI:RUser Interaction
Required
Scope
S:CScope
Changed
Impact
C:HConfidentiality
High
I:NIntegrity
None
A:NAvailability
None
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Weaknesses

CWE-200

Affected Products

librechatlibrechat
Mixed
Communications / messaging-chat
LibreChatdanny-avila
Mixed
Communications / messaging-chat
librechatoss-projectCommunications
danny-avilaindividual-devCommunicationsaka danny-avila/librechat, librechat

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Official Patch Available

MITRE ATT&CK

1 technique
Collection
View detailed technique mapping

References

https://github.com/danny-avila/LibreChat/security/advisories/GHSA-pmw7-gqwj-f954
github.com

Timeline

Published
Mar 27, 2026
Last Updated
Mar 30, 2026

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